Antibody Dependent Cell mediated Cytotoxicity "ADCC"
Definition:
It is a mechanism of cell-mediated immunity whereby an effector cell of the immune system actively lyses a target cell that has been bound by specific antibodies.
It is one of the mechanisms through which antibodies, as part of the humoral immune response, can act to limit and contain infection.
Classical ADCC is mediated by:
Natural killer (NK) cells.
Monocytes "Macrophages".
Eosinophils.
ADCC by NK cells:
NK cells are capable of antibody-dependent cellular cytotoxicity or ADCC. NK cells have receptors on their surface for the Fc portion of IgG. When the antibody IgG is made against epitopes on "foreign" membrane-bound cells, e.g., virus-infected cells and cancer cells, the Fab portions of the antibodies react with the "foreign" cell. The NK cells then bind to the Fc portion of the antibody.
The NK cell then releases pore-forming proteins called perforins, proteolytic enzymes called granzymes, and chemokines. Granzymes pass through the pores and activate the enzymes that lead to apoptosis of the infected cell by means of destruction of its structural cytoskeleton proteins and by chromosomal degradation. As a result, the cell breaks into fragments that are subsequently removed by phagocytes. Perforins can also sometimes result in cell lysis. (When NK cells are carrying out ADCC, they are sometimes also referred to as killer cells.)
Eosinophils can also mediate ADCC. For example, eosinophils can kill certain parasitic worms known as helminths through ADCC. ADCC is part of the adaptive immune response due to its dependence on a prior antibody response.
يعني ببساطة:
هي عملية قتل للخلية الغريبة عن طريق وسيط " اللي هوا ال Ab"
كل دور ال Ab انه يمسك الخليه الغريبة لكنه لا يستطيع فعل اي شئ اكتر من ذلك
ولأن لل Ab مستقبل "Fc receptor" علي سطح بعض الخلايا فممكن ان يرتبط بيها
يعني كده الا Ab هايكون ماسك الخلية الغريبة من ناحية "by Fab"
وماسك ال خلية اللي هاتقوم بعملية القتل من ناحية تانية "By Fc"
وده بيخلق اشارة قوية جوة ال NK يخليها تبدأ تفرز ما بداخلها لقتل الخلية الغريبة
Perforins.........خرامات تقوم بعمل فتحات في سطح الخلية مما يؤدي الي دمارها نهائيا
Granzymes........ عبارة عن مجموعه من الانزيمات اللي بتدخل جوه الخلية وتبدأ عملية ال Apoptosis
اما في حالة ال eosinophils فالوضع مختلف شوية
لأن الخلية الغريبة مش بتكون خلية واحده دي بتكون دوده في الاغلب
ولما بتحصل عملية الارتباط اللي حكينا عنها ده بيؤدي الي افراز ال eosinophils لكل محتوياتها القاتلة للدوده
The Fab portion of the antibody binds to epitopes on the "foreign" cell. The NK cell then binds to the Fc portion of the antibody. The NK cell is then able to contact the cell and release pore-forming proteins called perforins, proteolytic enzymes called granzymes, and chemokines. Granzymes pass through the pores and activate the enzymes that lead to apoptosis of the infected cell by means of destruction of its structural cytoskeleton proteins and by chromosomal degradation. As a result, the cell breaks into fragments that are subsequently removed by phagocytes. Perforins can also sometimes result in cell lysis.
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والله الموفق
د.أحمد رمزي
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